1. Field of the Invention
The present invention relates to a spin valve thin film magnetic element and a thin film magnetic head, and particularly to a spin valve thin film magnetic element and a thin film magnetic head in which the rate of change in magnetoresistance can be increased.
2. Description of the Related Art
Magnetoresistive magnetic heads include a MR (Magnetoresistive) head comprising an element exhibiting a magnetoresistive effect, and a GMR (Giant Magnetoresistive) head comprising an element exhibiting a giant magnetoresistive effect. In the MR head, the element exhibiting a magnetoresistive effect has a single layer structure comprising a magnetic material. On the other hand, in the OMR head, the element exhibiting a magnetoresistive effect has a multilayer structure in which a plurality of materials are laminated. Although there are several types of structures creating the giant magnetoresistive effect, a spin valve thin film magnetic element has a relatively simple structure and exhibits a high rate of change in resistance with an external magnetic field.
Recently, high-density magnetic recording has been increasingly demanded, and a spin valve thin film magnetic element adaptable for higher recording density has increasingly attracted attention.
A conventional spin valve thin film magnetic element is described with reference to the drawings. FIG. 25 is a schematic sectional view showing a conventional spin valve thin film magnetic element 101 as viewed from the magnetic recording medium side, and FIG. 26 is a schematic sectional view showing the conventional spin valve thin film magnetic element 101 as viewed from the track width direction.
Furthermore, shield layers are formed above and below the spin valve thin film magnetic element 101 with gap layers provided therebetween to form a reproducing thin film magnetic head comprising the spin valve thin film magnetic element 101, the gap layers and the shield layers. A recording inductive head may be laminated on the thin film magnetic head.
The thin film magnetic head is provided at the trailing side end of a floating slider together with the inductive head to constitute a thin film magnetic head which detects a recording magnetic field of a magnetic recording medium such as a hard disk or the like.
In FIGS. 25 and 26, the Z direction coincides with the movement direction of the magnetic recording medium, the Y direction coincides with the direction of a leakage magnetic field from the magnetic recording medium, and the X1 direction coincide with the track width direction of the spin valve thin film magnetic element 101.
The spin valve thin film magnetic element 101 shown in FIGS. 25 and 26 is a bottom-type single spin valve thin film magnetic element comprising an antiferromagnetic layer 103, a pinned magnetic layer 104, a nonmagnetic conductive layer 105, and a free magnetic layer 111, which are laminated in turn.
In FIGS. 25 and 26, reference numeral 100 denotes an insulating layer made of Al2O3 or the like, and reference numeral 102 denotes an underlying layer made of Ta (tantalum) or the like and laminated on the insulating layer 100. The antiferromagnetic layer 103 is laminated on the underlying layer 102, the pinned magnetic layer 104 is laminated on the antiferromagnetic layer 103, and the nonmagnetic conductive layer 105 made of Cu or the like is laminated on the pinned magnetic layer 104. Furthermore, the free magnetic layer 111 is laminated on the nonmagnetic conductive layer 105, and a capping layer 120 made of Ta or the like is laminated on the free magnetic layer 111.
In this way, the layers from the underlying layer 102 to the capping layer 120 are laminated in turn to constitute a laminate 121 having a substantially trapezoidal sectional shape having a width corresponding to the track width.
The pinned magnetic layer 104 is made of, for example, a NiFe alloy or the like, and laminated in contact with the antiferromagnetic layer 103. Therefore, an exchange coupling magnetic field (exchange anisotropic magnetic field) occurs in the interface between the pinned magnetic layer 104 and the antiferromagnetic layer 103 to pin the magnetization direction of the pinned magnetic layer 104 in the Y direction shown in the drawings.
The free magnetic layer 111 comprises a nonmagnetic intermediate layer 109, and first and second free magnetic layers 110 and 108 formed with the nonmagnetic intermediate layer 109 provided therebetween. The first free magnetic layer 110 is provided on the capping layer 120 side of the nonmagnetic intermediate layer 109, and the second free magnetic layer 108 is provided on the nonmagnetic conductive layer 105 side of the nonmagnetic intermediate layer 109.
The thickness t1 of the first free magnetic layer 110 is smaller than the thickness t2 of the second free magnetic layer 108.
The first free magnetic layer 110 is made of a ferromagnetic material such as a NiFe alloy or the like, and the nonmagnetic intermediate layer 109 is made of a nonmagnetic material such as Ru or the like.
The second free magnetic layer 108 comprises a anti-diffusion layer 106 and a ferromagnetic layer 107. Each of the anti-diffusion layer 106 and the ferromagnetic layer 107 comprises a ferromagnetic material, and for example, the anti-diffusion layer 106 is made of Co, and the ferromagnetic layer 107 is made of a NiFe alloy. The first free magnetic layer 110 and the ferromagnetic layer 107 are preferably made of the same material.
The anti-diffusion layer 106 is provided for preventing mutual diffusion between the ferromagnetic layer 107 and the nonmagnetic conductive layer 105.
The first free magnetic layer 110 and the second free magnetic layer 108 are antiferromagnetically coupled with each other. In other words, when the magnetization direction of the first free magnetic layer 110 is oriented in the X1 direction shown in the drawings by bias layers 132, the magnetization direction of the second free magnetic layer 108 is oriented in the direction opposite to the X1 direction.
Since the first and second free magnetic layers 110 and 108 have the thickness relation t1<t2, magnetization of the first free magnetic layer 110 remains so that the magnetization direction of the entire free magnetic layer 111 is oriented in the X1 direction.
In this way, the first free magnetic layer 110 and the second free magnetic layer 108 are antiferromagnetically coupled with each other so that the magnetization directions are antiparallel to each other to create a synthetic ferrimagnetic state (synthetic ferrimagnetic free).
Therefore, the magnetization direction of the free magnetic layer 111 crosses the magnetization direction of the pinned magnetic layer 104.
The bias layers 132 made of, for example, a Co—Pt (cobalt-platinum) alloy are formed on both sides of the laminate 121. The bias layers 132 orient the magnetization direction of the first free magnetic layer 110 in the X1 direction to bring the free magnetic layer 111 in a single magnetic domain state, suppressing Barkhousen noise of the free magnetic layer 111.
Reference numeral 134 denotes a conductive layer made of Cu or the like.
Furthermore, bias underlying layers 131 made of, for example, a nonmagnetic metal such as Cr are provided between the bias layers 132 and the insulating layer 100, and between the bias layer 132 and the laminate 121.
Furthermore, intermediate layers 133 made of, for example, a nonmagnetic metal such as Ta or Cr are provided between the bias layers 132 and the conductive layers 134.
In the spin valve thin film magnetic element 101, when the magnetization direction of the free magnetic layer 111, which is oriented in the X1 direction, is changed by a leakage magnetic field from the recording medium such as a hard disk or the like, the electric resistance changes with the relation to magnetization of the pinned magnetic layer 104 which is pinned in the Y direction, and the leakage magnetic field form the recording medium is detected by a voltage change based on the change in the electric resistance.
The free magnetic layer 111 comprises the first and second free magnetic layers 110 and 108 antiferromagnetically coupled with each other, and the magnetization direction of the entire free magnetic layer 111 changes with an external magnetic field of small magnitude, thereby increasing the sensitivity of the spin valve thin film magnetic element 101.
The above-described spin valve thin film magnetic element 101 comprises the free magnetic layer 111 comprising the first and second free magnetic layers 110 and 108 put into the ferrimagnetic state, and exhibits a high rate of change in magnetoresistance when the thickness of the second free magnetic layer is 3 to 4 nm. However, in this case, the resistance of the spin valve thin film magnetic element is increased to cause the problem of decreasing reproduced output.
It is thought that a further improvement in the magnetic recording density will be required in future, and a spin valve thin film magnetic element having a higher rate of change in magnetoresistance is demanded.